Severe wind conditions such as clear air turbulence encounters by general and commercial aviation continue to pose significant safety and flight efficiency concerns. Almost anyone who has flown commercially has had an unpleasant experience with turbulence. According to some estimates, turbulence encounters account for well over 75% of all weather-related injuries on commercial aircraft and amount to at least $200 M annually in costs due to passenger and crew injuries and aircraft damage. Of particular interest is clear-air turbulence (CAT) which is the turbulent movement of air masses in the absence of any visual clues, such as clouds, and is caused when bodies of air moving at widely different speeds meet. The atmospheric region most susceptible to CAT is the high troposphere at altitudes of around 7,000-12,000 meters (23,000-39,000 ft) as it meets the tropopause. Here CAT is most frequently encountered in the regions of jet streams. At lower altitudes it may also occur near mountain ranges. Consequently, there is an urgent need to provide accurate and real-time wind/turbulence predictions, particularly CAT, and courses-of-actions to meet the needs of aviation communities.
However the real-time information about the current turbulent state of the atmosphere required by pilots and dispatchers for making tactical en-route decisions is not adequately provided via the FAA's thunderstorm avoidance guidelines, by currently operational turbulence forecasts, or by future systems such as such as the Graphical Turbulence Guidance (GTG) “Nowcast” (N-GTG) at NCAR slated to combine turbulence observations, inferences and forecasts to produce new turbulence assessments approximately every 15 minutes.
Light detection and ranging (lidar) systems have been developed that are capable of remotely measuring range-resolved wind speeds for use in various applications, including but not limited to weather forecasting, air quality prediction, air-traffic safety, and climate studies. In general, lidar operates by transmitting light from a laser source to a volume or surface of interest and detecting the time of flight for the backscattered light to determine range to the scattering volume or surface.
A Doppler wind lidar also measures the Doppler frequency shift experienced by the light scattered back to the instrument due to the motions of molecules and aerosols (e.g. particles and droplets) in the atmospheric scattering volumes, which is directly tied to the speed of the wind in that volume, relative to the lidar line of sight (LOS). The wind speed along the LOS is determined by projecting the wind speed and direction (the wind vector) onto that LOS.
One potential application for wind lidar systems is in connection with the detection of atmospheric turbulence. As noted, atmospheric turbulence is a primary cause of weather related injuries to aircraft passengers and flight crews. Accordingly, detecting atmospheric turbulence is of great interest. However, systems for detecting turbulence, and in particular clear air turbulence, that can be carried by aircraft have been unavailable. In particular, a system that was compact and that provided a suitably wide field of view that could be deployed in a conventional aircraft has been unavailable.